1. Field of the Invention
The present invention relates generally to support equipment for an agricultural apparatus, and in particular to a suspension system for a spray boom applicator.
2. Description of the Related Art
Open ground is often treated with various chemicals to effect the growth of vegetation. Agricultural fields are typically treated with either dry or liquid chemicals such as fertilizers, herbicides, fungicides, insecticides, etc. Application of liquid chemicals is frequently accomplished using boom spraying equipment. Boom spraying equipment typically consists of a length of rigid support structure (e.g., a boom sprayer) that is attached to and extends laterally from a vehicle, such as a self propelled or towed terrestrial vehicle. As the boom sprayer traverses the surface of a field, the liquid chemical is ejected from liquid spray nozzles spanning the length of boom. The optimal boom height is determined by such factors as the spray pattern of the nozzle, the material being applied, wind conditions, crop heights, etc.
Applying chemicals using boom sprayers is very effective because utilization of long boom lengths permits application of a precise amount of chemical to a target while minimizing the number of passes the equipment needs to make to treat a given area. Therefore, it is desired for the boom to maintain a fixed height above the target to ensure proper application of the chemical. This results in an economic benefit whereby excessive application of the chemical is minimized, and the task is completed in less time.
Boom sprayers used in agricultural operations are subject to factors that can compromise economic and operational efficiencies. Spraying systems are usually directly attached to a vehicle that travels on the ground being treated by a mechanism that allows for adjustment of the height of the boom sprayer above the target. Often the systems use booms that may extend up to 40 feet from each side of the vehicle, e.g., defining swath widths of up to 90 feet. As a result, when the vehicle encounters irregularities in the surface, the vertical accelerations of the vehicle are transmitted to the boom sprayer through the attachment mechanism. The distal ends of the boom experience high vertical accelerations resulting in a large amplitude of travel beyond the desired height above the target due to their distance from the attachment mechanism and flexing of the supporting structure. The resulting forces put stress upon the vehicle, attachment mechanism, and boom sprayer, causing fatigue and wear of the equipment. Further, vertical movement of the boom sprayer above the target decreases the effectiveness of the application by causing inconsistent application of the chemical.
These problems have been addressed by providing a combination of mechanisms that isolate the movement of the vehicle from the boom. For example, the Thorstensson U.S. Pat. No. 5,373,767 discloses a cushion suspension system for an agricultural tool which utilizes a hydraulic cylinder in conjunction with an air spring to provide dampening of the vertical movement transmitted to the tool caused by movement of the attached vehicle. The Guesdon U.S. Pat. No. 6,315,218 discloses a suspension device for a boom sprayer which utilizes the articulation among rocker arms, link rods, and hydraulic cylinders to dampen the vertical movement of a boom sprayer caused by vertical movement of the vehicle chassis. However, a disadvantage of such combined systems relates to their complexity of implementation and adjustability of performance.
Heretofore there has not been available a variable dampening rate suspension system for a boom sprayer with the advantages and features of the present invention.